Reports of both a high incidence of spontaneous abortion among operating room personnel and embryolethal and teratogenic effects of high concentrations of anesthetics in certain animals suggests a possible relationship between the operating room related abortions and chronic exposure to low concentrations of anesthetic gases in the operating room environment. Groups of pregnant rats will be subjected to both acute-high dose exposures and chronic-low dose exposures of anesthetic gases to study the possible embryolethal and/or teratogenetic effects of such exposures in rats. Acute high dose experiments will subject groups rats to 4-hour anesthetic exposures. Separate groups will be exposed day 8, 9. 10, 11, 12, 13, 14, and 15 of the pregnancy. Chronic low dose experiments will subject groups of rats of 8-hour daytime, 8 hour nighttime, or 24 hour/day anesthetic exposures daily from days 8-15 of the pregnancy. Animals will be sacrificed and examined on day 20 of the 21 day pregnancy. Data subjected to statistical analysis will include the incidence of 1) abnormal litters, 2) abnormal fetuses/litter, 3) specific congenital anomalies, and 4) fetal mortality. The chronic exposure studies will also be analyzed to determine whether differences exist with 8 hr. vs. 24 hour exposure, and whether a diurnal variation in the effects exists.